A threatening snapshot? The conservation status of Australian land snails

AMRI conservation assessment reveals worrying trend for Australian land snails, with several species threatened and one perhaps extinct.

Let’s go back a century and a bit, to the late 1800s. In the small, then thriving town of Mossgiel in western New South Wales, blackened rain clouds are moving toward a flat horizon. Hooves are splashing in newly laid puddles, leaving bystanders mud-flecked in their Sunday best as a Cobb & Co stagecoach rattles by. And why not cast our eyes to the ground? It just might be that if we do, we’ll notice individuals of the lyrically named land snail Sinumelon simulante (or Mossgiel Dwarfmelon) moving immeasurably slowly under the weight of their tan, dome-shaped shells, as they tentatively come out of hiding to take advantage of the rare downpour.

Just as this scene is long gone and now a fading memory, so are the snails. Because hypothetical as the above may be, it may have been the event playing out the very last time living specimens of the Mossgiel Dwarfmelon were seen. More than three-quarters of a century later - following decades of widespread land clearing, heavy grazing, and major droughts causing sparse vegetation to shrivel up and scatter with the wind - old and sun-bleached shells, their inhabitants long gone, were encountered not too far from Mossgiel. That find dates back to 1972, and constitutes the last proof of existence that we have for this species. Not a single shell has been recorded in the four and a half decades since.

You guessed correctly – the Mossgiel Dwarfmelon may have gone extinct. However, because its potential historical distribution covered a large area, there is still a slim chance that some individuals persist in small remnant pockets of suitable habitat. Although, given the travails mentioned above and the fact that nearly all of its former documented range is now used for grazing and agriculture, too much optimism is hardly warranted.

Extinct or not, that question is very hard to answer definitively. Should it still exist it is certainly threatened, although you won’t find it on the official Red List of threatened species. Of the more than two thousand land snail species known in Australia, only a fraction has been listed to date. This, importantly, reflects the number of conservation assessments done so far and by no means the actual number of threatened species. Through the current evaluation of the conservation status of more than 700 Australian land snails (read more about it here), we are now striving to get a more comprehensive understanding of the status quo in land snail conservation. Through our assessments, a picture is starting to emerge: one where dozens of additional species are likely threatened, ranging from Vulnerable to Critically Endangered following the prescribed categories of the International Union of the Conservation of Nature (IUCN).

So, in addition to the hapless Mossgiel Dwarfmelon, what others have we come across so far? The Boggabri and Jimbour Black Soil Snails, Liverpool Range Bristle Snail, Port Lincoln Shrubland Snail, Mount Coot-tha Bristle Snail and Maroubra Woodland Snail, to name a few, are all likely candidates for the official Red List. The Maroubra Woodland Snail (Meridolum maryae) exists right here on our doorstep – confined to coastal dunes and headlands of the Sydney metropolitan area, it has been subject to enormous urbanisation pressure, invasion by the African ‘Bitou’ bush and other disturbances, leaving the remaining population dwindling and fragmented. In Brisbane, the Mount Coot-tha Bristle Snail is imperilled by the displacement of native habitat by the destructive buffel grass, whereas further inland the Black Soil snails have the misfortune of favouring native grassland on volcanic black soil, a substrate so suited for agriculture that extremely little of it remains. For the Jimbour Black Soil Snail, the situation is so dire that it is possibly teetering on the brink of extinction, with the Boggabri species in all likelihood not too far behind unless effective protection measures are put in place.

Whereas habitat loss through land clearing is the main threat in southern Australia, pastoralism, invasive weeds and large-scale habitat alteration due to the so-called ‘grass-fire cycle’ are major concerns in the north. The latter is a particularly worrying process, converting enormous areas of woodland into savannah as the spread of tall, highly combustible grasses provides an ever-increasing fuel load. The fires, now burning hotter and more frequently as these grasses advance, lay waste to native trees and vine thickets, in turn furthering the spread of grass-dominated savannah. This well-documented vicious cycle causes untold harm to land snails and many other animals and plants.

Of course, it is not all bleak. Many species we have assessed are not of particular concern, often thanks to the prescience of those who designate national parks and other protected areas, conservation-minded landowners and community groups, and many other involved citizens and organisations. And while the evaluation process is not exhaustive – we need more data for that – it provides a valuable snapshot of the wellbeing of an entire fauna, and hopefully also a crucial roadmap to show us where future conservation efforts are most needed.

Hopefully, it won’t lead to another Mossgiel.

Dr Anders Hallan, AMRI Scientific Officer
Dr Frank Köhler, AMRI Senior Research Scientist
Michael Shea, AMRI Technical Officer